The present application is related to the U.S. Pat. No. 4,503,821 commonly assigned and patented Mar. 12, 1985.
This invention relates generally to an apparatus and method for controlling an amount of fuel injected into engine cylinders respectively so that torque generated by respective cylinders is uniform throughout the cylinders.
The amount of fuel injected into a multi-cylinder internal combustion engine has been conventionally controlled uniformly throughout all the cylinders in both gasoline engines and diesel engines. According to known electronic fuel injecting systems for gasoline engines, the valve-opening duration of electromagnetic valves respectively provided to individual cylinders is controlled such that the valve opening duration is common to all the cylinders. In known electronically controlled diesel engines, which have been recently put in practical application stage, the position of an injection amount-controlling member, such as a control rack or a spill ring, is controlled where the controlling member is common to all the cylinders.
Although such a control effected uniformly throughout all the cylinders of an engine is simple, there arises a problem of variation or scattering in injecting fuel amount throughout the cylinders. Therefore, in conventional apparatus high manufacturing precision is required when manufacturing various parts, such as injection valves, injection conduits or the like, used in the injection system to reduce such variation throughout the cylinders. Such high manufacturing precision or accuracy necessarily increass the manufacturing cost. Furthermore, even though the precision of used parts have been increased to its limit so that variation throughout cylinders is minimized, the amount of fuel actually injected into engine cylinders has a chance to suffer from variation or scatter throughout cylinders due to secular change or external disturbance, such as a variation in actuating timing of intake and/or exhaust valves or the like.
Such variation in amount of fuel inejected into cylinders of an engine results in irregular rotation of the engine crankshaft. Especially, during idling such irregular rotation is uncomfortable and noisy. Generally speaking, the engine rotational speed during idling is set to a low value in view of suppression of fuel consumption. On the other hand, it is desired, especially for passenger automobiles, that engine rotation during idling is as smooth as possible thereby providing a comfortable environment. Particularly, the above-mentioned irregular rotation during idling is desired to be reduced to achieve stable engine rotation.
To solve this problem, a method was proposed in a Japanese patent provisional publication No. 58-214627 such that the variation in rotational speed around fuel injection in each cylinder is detected first and the amount of fuel to be injected is corrected so that the variation in engine speed becomes uniform, thereby establishing a uniform combustion state in all the cylinders.
However, since this correction control is performed through digital processing using a microcomputer or the like, rounding error due to digit compression is inevitable while there are some other errors caused from variations in the characteristics of various sensors. Such errors occur in each correction of the amount of fuel to be injected for each cylinder, and thus the sum total of the errors of the correction amount for all the cylinders does not necessarily equal zero. This sum total of errors may assume either a positive or negative value, and since each error occurs in each time of correction independent of other error occurring in other correction, it is expected that errors are accumulated as the number of corrections increases in view of stochastic process. As a matter of fact, the sum total of such errors are accumulated in sequence to provide a great absolute value which affects the total amount of fuel supplied to the engine. As a result, engine rotational speed, emission of noxious components, drivability of the automobile equipped with the engine, and the performance of the engine are apt to be undesirably influenced.